Liquid Adhesive

ABSTRACT

A low-expanding adhesive composition comprising: a diisocyanate, a surfactant and an activator is provided. The provided adhesive composition cures upon exposure to water. The adhesive composition can be used to bond wood, metal, glass, ceramic, leather, acrylic, PVC and combinations thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application takes priority from U.S. provisional application Ser.No. 60/744,250 filed Apr. 4, 2006, which is incorporated by referenceherein to the extent not inconsistent with the disclosure herewith.

BACKGROUND OF THE INVENTION

Urethane adhesives are known in the art (Modern Plastics Encyclopedia,McGraw-Hill, New York, N.Y.). Urethane adhesives can provide a verystrong bond between surfaces to be joined, and they adhere to a widevariety of surface materials including wood, metal, ceramics, glass,most fabrics, leather and most plastics except high density linearpolyethylene, polypropylene and Teflon. In addition, urethane adhesivescan be provided to the end user as a single component, a stable,flowable liquid having a stable shelf life but capable of curing withinminutes when contacted with water, a hygroscopic material, or humid air.Some examples of moisture-cured urethane adhesives include U.S. Pat.Nos. 5,698,656; 6,657,035; 6,368,714; 5,668,222; and WO 00/44847.

It is well known that most urethanes expand during the curing processbecause the curing reaction yields CO₂ gas which remains entrainedwithin the urethane polymer matrix. Many applications of urethaneadhesives are specifically designed to exploit the property of expansionduring curing, which is advantageous when surfaces to be joined arerough, irregular or contain gaps or holes that make them difficult tobond.

While useful under certain circumstances, the property of expansionduring curing can also be a drawback which has limited the utility ofurethane adhesives for applications where it is desired to maintain athin bond line between the surfaces to be joined. Examples of suchapplications include woodworking, manufacturing, laminating and thelike. For these applications, as well as others, it would be desirableto have a low-expanding urethane adhesive.

SUMMARY OF THE INVENTION

The present invention provides a urethane adhesive that can be used forapplications where conventional expanding urethane adhesives areunsuitable.

More specifically, provided is a moisture-activated adhesive compositioncomprising: (a) an aromatic diisocyanate; (b) an activator; and (c) asilicon surfactant. In one embodiment, the percentages by weight of thecomponents in the moisture-activated adhesive composition are 95% orgreater by weight of an aromatic polyisocyanate, 1% or less by weight ofan activator, and 5% or less by weight of a silicon surfactant. In aparticular embodiment, the percentages by weight of the components inthe moisture-activated adhesive composition are: 98.85-95.2% by weightRubinate 9511; 0.15-0.8% by weight DMDEE; and 1-4% by weight SAG 47. Inparticular embodiments, the moisture-activated adhesive compositioncomprises, consists essentially of, or consists of: 97.2% by weightRubinate 9511; 0.3% by weight DMDEE; and 2.5% by weight SAG 47.

Also provided is a method for bonding surfaces together comprising:applying to a first surface a moisture-activated adhesive compositiondisclosed herein; contacting said first surface with a second surface;and curing the adhesive composition. As used herein, “bonding” means thesurfaces are permanently or semi-permanently attached, so that thesurfaces will not separate until application of a desired level offorce.

The curing step can be performed in different ways, depending on theenvironment where the adhesive composition is being used, as well as thesurfaces which are being bonded. For example, one or more surfaces canbe sprayed with water or an aqueous substance. Alternatively or incombination, the bonding method can be performed in a humid environment,defined as one having sufficient humidity for the reaction to occur tothe desired extent. In one example, a humid environment has above 5%relative humidity. There may be an optional “setting” step where theadhesive is allowed to set before the surfaces are attached, allowingsome portion of any CO₂ that is generated to escape.

Also provided is a method for making a moisture-activated adhesivecomposition comprising combining: (a) between 98.85 and 95.2% by weightRubinate 9511; (b) between 0.15 and 0.8% by weight DMDEE; and (c)between 1 and 4% by weight SAG 47. In a particular embodiment, 97.2% byweight Rubinate 9511; 0.3% by weight DMDEE; and 2.5% by weight SAG 47are combined to make the moisture-activated adhesive composition.

DETAILED DESCRIPTION OF THE INVENTION

The invention is further described by the following non-limitingexamples:

Aromatic diisocyanates useful in the invention are those which in theirmonomer form have one or more aromatic functionalities and twoisocyanate functionalities. Specific examples of aromatic diisocyanatesuseful in the invention include, e.g., p-phenylene diisocyanate;m-phenylene diisocyanate; 2,4-toluene diisocyanate; 2,6-toluenediisocyanate; 2,4′-diphenyl methane diisocyanate (2,4′-MDI) ;4,4′-diphenylmethane diisocyanate (4,4′-MDI); and mixtures thereof.

One example of a useful aromatic diisocyanate is a MDI, such as Rubinate9511. Rubinate 9511 is a commercially available pre-polymerized resin of3000-5000 average MW manufactured by Huntsman Chemical Company Detroit,Mich. If the molecular weight of the resin is too low, the adhesivecomposition becomes elastic. If the molecular weight of the resin is toohigh, the adhesive composition becomes brittle. The monomeric chemicalcomposition is principally methylene diphenyl 4,4′-di isocyanate(hereinafter “4,4′-MDI”). Rubinate 9511 also contains small percentagesof 2,4′-diisocyanate and 2,2′-diisocyanate isomers. Alternatively, a TDI(toluene diisocyanate) can be used, as known in the art. Commercial TDIproducts are a mixture of the 2,4′- and 2,6′-isomers.

One useful MDI resin is 4,4′-MDI, with the amounts of 2,2′- MDI and2,4′-MDI minimized to the extent consistent with cost and commercialavailability. As the content of 4,4′-MDI is increased, the flexibilityof the cured resin is increased. In most applications, the bondedmaterials are themselves capable of flexing to some extent, and the bondjoining the materials is preferably flexible to a similar extent.

Activators (also known as catalysts) useful in curing reactions areknown in the art. One such activator is DMDEE or similar materials.DMDEE is 2′-Dimorpholino diethyl ether, available from, e.g. HuntsmanChemical Co., Detroit, Mich. DMDEE is the primary catalyst used herein,typically described as a fast-blowing catalyst which is used extensivelyin the manufacture of many polyurethanes. Materials similar to DMDEEinclude those wherein the diethyl ether groups are replaced withdi(alkyl) ether groups having from 1 to 6 carbons in each alkyl chain.

Useful silicon surfactants include dimethylsiloxanes, andpolydimethylsiloxanes. One such useful silicon surfactant is SAG 47,available from General Electric, Uniontown, W. Va.

The amount of Rubinate 9511, in terms of percent by weight can beadjusted as desired, to compensate for variation in the amounts of DMDEEand SAG 47 used in the formulation. The effect of increasing the amountof DMDEE is to shorten the curing time and to reduce the time forworking with the parts to be joined. The practical working time isconveniently assessed by the time in which the curing process results inthe adhesive becoming tacky, or begins to set. The time to tack is anapproximate measure of the time available for joining and clamping to bedone without sacrificing bond strength.

Various tests are used by those of skill in the art to measure time totack in a reproducible fashion. At 0.3% by weight DMDEE, for example,the described adhesive becomes tacky in about 30 minutes, which isconsidered optimal for hand-operated joining and clamping operations.About 15 minutes tack time can be achieved using 0.7% by weight DMDEE,which could be advantageous for automated processes such as lamination.

The quantity of SAG 47 can also be varied, as desired, for the desiredcharacteristics of the adhesive. The lower limit is governed byexpansion of the adhesive during curing. A criterion used herein is thatno increase in bond thickness should occur during curing when two 4 inchby 6 inch blocks of wood are coated with adhesive and clamped. Reductionin bond strength can occur at increased levels of SAG 47, the practicalupper limit being about 4.0% by weight.

All variations in DMDEE and SAG 47 content are compensated by adjustmentof the MDI content, to yield a sum of 100% by weight of all components.

Optimally, a water scavenger, such as p-toluenesulfonyl isocyanate(PTSI) can be included in the formulation at 1% or less by weight, tofurther stabilize the formulation and to prevent premature curing causedby residual water which might be present in other components.

Other optional additives, such as processing additives, fungicides,tackifiers, adhesion promoters, flame retardants, anti-oxidants,ultraviolet light stabilizers, fillers and combinations thereof may beadded. These additives may be added in any suitable amount, andpreferably are present in an amount less than 1% by weight.

The adhesive compositions of the invention are designed to have lowexpansion. In particular embodiments, the adhesive compositions of theinvention have unconstrained expansion of a maximum of 300% by volume,in comparison to prior known adhesive compositions which commonly haveunconstrained expansion in excess of 1000% by volume. Unconstrainedexpansion means there is no clamping used during a bonding process. Thecuring temperature is any suitable temperature. Room temperature may beused. As will be apparent by one of ordinary skill in the art, atemperature above the water freezing point should be used because wateris the catalyst in the process.

The adhesive of the present invention is provided as a flowable liquid.The adhesive of the present invention is stable (remains uncured) for atime measured in months or years. In certain embodiments, the adhesiveof the present invention is stable in a bottle at room temperature forover a year. The quantity of adhesive to be dispensed can be controlledby hand or mechanical means. The surfaces to be joined can be clampedtogether and allowed to cure, the resulting bond line being essentiallyas thin as desired without sacrificing the strength typical of urethaneadhesive bonds.

The adhesive composition can be used to bond many substances andcombinations of substances (where one surface is one material andanother surface is a different material). Some examples of thesubstances which can be bonded include: wood, metal, glass, ceramic,leather, acrylic, PVC and combinations thereof.

The surfaces to be bonded can be sanded before use and cleaned, ifnecessary, with alcohol, or other solvent to remove particulate matteror foreign substances such as oil or dirt. After application of theadhesive composition, the surfaces can be clamped, if necessary, usingany suitable clamping method, as known in the art. The adhesivecomposition can be painted or sanded after curing, if desired.

EXAMPLE 1 Formulation Example

Table 1 lists one exemplary formulation of the urethane adhesive of theinvention.

TABLE 1 Material Percent by Weight Grams per Batch Rubinate 9511 97.219440.00 DMDEE 0.3 60.00 SAG 47 2.5 500.00 Total 100.00 20000.00

EXAMPLE 2 Mixing Example

The following example describes preparation of a five gallon batch ofthe urethane adhesive.

Weighing

1. Weigh out 19440 grams of Rubinate 9511 into a clean 5 gallon plasticbucket.2. Weigh out 60 grams of DMDEE into a clean plastic cup.3. Weigh out 500 grams of SAG 47 into a clean plastic cup.4. Set aside until ready to mix.

Mixing (Mix at ≦5% Relative Humidity)

1. In the 5 gallon bucket containing the Rubinate 9511 add 60 grams ofDMDEE and 500 grams of SAG 47.2. Place the bucket in the low shear Myers mixer.3. Start the mixer and mix for 60 minutes.4. After mixing put cover on the 5 gallon container and set aside untilready to package.

All mixing operations were carried out at room temperature in anatmosphere of air having no more than 5% relative humidity to minimizethe potential for premature curing.

The process can be scaled up easily, as known in the art. For example,if a continuous mixture process is used, the three components arecombined together in the proper volume ratio and passed into a staticmixer.

The foregoing specific embodiment is an example of a urethane adhesiveof the invention. Other embodiments within the scope of the inventioncan be formulated by those skilled in the art, following the teachingsand principles set forth herein.

Every formulation or combination of components described or exemplifiedcan be used to practice the invention, unless otherwise stated. Specificnames of compounds are intended to be exemplary, as it is known that oneof ordinary skill in the art can name the same compounds differently.One of ordinary skill in the art will appreciate that methods, uses andcomponents other than those specifically exemplified can be employed inthe practice of the invention without resort to undue experimentation.All art-known functional equivalents, of any such methods, uses andcomponents are intended to be included in this invention. Whenever arange is given in the specification, for example, a compositioncomponent weight range, all intermediate ranges and subranges, as wellas all individual values included in the ranges given are intended to beincluded in the disclosure to the extent as if individually listed.

As used herein, “comprising” is synonymous with “including,”“containing,” or “characterized by,” and is inclusive or open-ended anddoes not exclude additional, unrecited elements or method steps. As usedherein, “consisting of” excludes any element, step, or ingredient notspecified in the claim element. As used herein, “consisting essentiallyof” does not exclude materials or steps that do not materially affectthe basic and novel characteristics of the claim. Any recitation hereinof the term “comprising”, particularly in a description of components ofa composition or in a description of elements of a device, is understoodto encompass those compositions and methods consisting essentially ofand consisting of the recited components or elements. The inventionillustratively described herein suitably may be practiced in the absenceof any element or elements, limitation or limitations which is notspecifically disclosed herein.

The terms and expressions which have been employed are used as terms ofdescription and not of limitation, and there is no intention in the useof such terms and expressions of excluding any equivalents of thefeatures shown and described or portions thereof, but it is recognizedthat various modifications are possible within the scope of theinvention claimed. Thus, it should be understood that although thepresent invention has been specifically disclosed by preferredembodiments and optional features, modification and variation of theconcepts herein disclosed may be resorted to by those skilled in theart, and that such modifications and variations are considered to bewithin the scope of this invention as defined by the appended claims.

In general the terms and phrases used herein have their art-recognizedmeaning, which can be found by reference to standard texts, journalreferences and contexts known to those skilled in the art. Thedefinitions are provided to clarify their specific use in the context ofthe invention.

All patents and publications mentioned in the specification areindicative of the levels of skill of those skilled in the art to whichthe invention pertains.

One skilled in the art would readily appreciate that the presentinvention is well adapted to carry out the objects and obtain the endsand advantages mentioned, as well as those inherent therein. Theadhesive composition components, percentages, uses and curing methodsdescribed herein are exemplary and are not intended as limitations onthe scope of the invention. Changes therein and other uses will occur tothose skilled in the art, which are encompassed within the spirit of theinvention, are defined by the scope of the claims.

Although the description herein contains many specificities, theseshould not be construed as limiting the scope of the invention, but asmerely providing illustrations of some of the embodiments of theinvention. Thus, additional embodiments are within the scope of theinvention and within the following claims. All references cited hereinare hereby incorporated by reference to the extent that there is noinconsistency with the disclosure of this specification. Some referencesprovided herein are incorporated by reference herein to provide detailsconcerning additional useful materials and additional uses of theinvention.

We claim:
 1. A moisture-activated adhesive composition comprising:98.85-95.2% by weight Rubinate 9511; 0.15-0.8% by weight DMDEE; and 1-4%by weight SAG
 47. 2. The moisture-activated adhesive composition ofclaim 1, wherein the percentages by weight of the components in themoisture-activated adhesive composition are: 97.2% by weight Rubinate9511; 0.3% by weight DMDEE; and 2.5% by weight SAG
 47. 3. Themoisture-activated adhesive composition of claim 1, consistingessentially of: 97.2% by weight Rubinate 9511; 0.3% by weight DMDEE; and2.5% by weight SAG 47
 4. The moisture-activated adhesive composition ofclaim 1, consisting of: 97.2 by weight Rubinate 9511; 0.3% by weightDMDEE; and 2.5% by weight SAG
 47. 5. A method for bonding surfacestogether comprising: applying to a first surface a moisture-activatedadhesive composition comprising: 98.85-95.2% by weight Rubinate 9511;0.15-0.8% by weight DMDEE; and 1-4% by weight SAG 47; contacting saidfirst surface with a second surface under curing conditions; and curingthe adhesive composition.
 6. The method of claim 5, wherein the curingstep is performed by applying water to at least one of the first andsecond surfaces.
 7. The method of claim 5, wherein the curing step isperformed by applying the adhesive composition in a humid environment.8. The method of claim 5, wherein the uncured adhesive has anunconstrained expansion of a maximum of 300% by volume when cured. 9.The method of claim 5, wherein the adhesive composition consists of:97.2% by weight Rubinate 9511; 0.3% by weight DMDEE; and 2.5% by weightSAG
 47. 10. The method of claim 5, wherein the surfaces are selectedfrom the group consisting of: wood, metal, glass, ceramic, leather,acrylic, PVC and combinations thereof.
 11. The method of claim 5,wherein the adhesive composition consists essentially of: 98.85-95.2% byweight Rubinate 9511; 0.15-0.8% by weight DMDEE; and 1-4% by weight SAG47.
 12. The method of claim 5, wherein the adhesive composition consistsof: 98.88-95.2% by weight Rubinate 9511; 0.15-0.8% by weight DMDEE; and1-4%by weight SAG
 47. 13. A method for making a moisture-activatedadhesive composition comprising combining the components: 98.85-95.2% byweight Rubinate 9511; 0.15-0.8% by weight DMDEE; and 1-4% by weight SAG47, to form a homogenous liquid.
 14. The method of claim 13, wherein thecomponents consist essentially of: 98.85-95.2% by weight Rubinate 9511;0.15-0.8% by weight DMDEE; and 1-4% by weight SAG
 47. 15. The method ofclaim 13, wherein the components consist of: 98.85-95.2% by weightRubinate 9511; 0.15-0.8% by weight DMDEE; and 1-4% by weight SAG
 47. 16.The method of claim 13, wherein the components consist of: 97.2% byweight Rubinate 9511; 0.3% by weight DMDEE; and 2.5% by weight SAG 47.